26S Proteasome-Dependent Control of Cytokinin Signaling

The Ubiquitin/268 Proteasome Pathway (UPP) controls the degradation of most intracellular proteins and is directly or indirectly implicated in the action of all plant hormones. Except for the cytokinin and jasmonate response pathways, UPP target proteins have been identified in all other hormone signal transduction cascades. We propose to identify the UPP targets of the cytokinin response pathway. The Arabidopsis mutant rpnl2a-1 carries a T-DNA insertional mutation in the gene encoding the 26S proteasome subunit RPNI2a. The rpnl2a-1 mutant is recessive and has decreased sensitivity to cytokinins, which suggests that a repressor of cytokinin responses is stabilized by the loss of268 proteasome function. We propose to (1) screen for mutations that suppress rpnI2a-l, (2) clone the suppressor loci and (3) analyze the functions of the identified proteins in cytokinin signaling and in UPP-dependent proteolysis. RELEVANCE TO NRI AND USDA STRATEGIC PLANS Cytokinins play a central role in cell division, shoot and root development, distribution of nutrients between plant organs, senescence and many other essential processes. Therefore, completion of this work may enhance economic opportunities for agricultural producers because it will generate new tools (1) to modify senescence processes for increasing shelf life of green biomass products, (2) to manipulate sink/source ratios for improving harvest indexes, (3) to generate marker-free plants and (4) to establish tissue culture procedures for micropropagation purposes.